To understand the regulating effect of exogenous nitric oxide on the plant physiological response on the stress condition of simulated acid rain, we examined the effects of exogenous nitric oxide with the donor of sodium nitroprusside i.e. SNP on the relative chlorophyll content, diurnal variations of photosynthesis and chlorophyll fluorescence with the experimental materials of Indocalamus barbatus McClure in 2007
The results showed as follows:（1) By treatment with exogenous nitric oxide(50-450 mg/L SNP),the decreases of relative chlorophyll content were significantly alleviated at the stress condition of pH 3.0 simulated acid rain,especially the treatment with 450mg/L sodium nitroprusside was the best.（2) Under the stress of simulated acid rain, the midday depression of photosynthesis became more serious. The daily average of net photosynthetic rate(Pn),stomatal conductance(Gs), transpiration rate(Tr) and stomatal limitation value(Ls) all were decreased significantly, while intercellular CO2 concentration(Ci) was increased. By treated with exogenous nitric oxide, Pn, Gs、Tr and Ls was increased at different extent, while Ci was decreased, especially the treatment with 450mg/L sodium nitroprusside was the most obvious .（3) Under the stress condition of simulated acid rain, the maximum fluorescence of dark adaptation(Fm),PSII maximal photochemical efficiency(Fv/Fm),PSII effective photochemical efficiency(Fv′/Fm′),maximum fluorescence of light adaptation(Fm′),stable fluorescence(Fs) photochemical quench(qP),non-photochemical quench(NPQ),PSII actual photochemical efficiency(ΦPSⅡ) and acyclic electron transfer rate(ETR) were all decreased, but the minimum fluorescence of dark adaptation(F0), and minimum fluorescence of light adaptation(F′0) were increased. After treated with 450 mg/L sodium nitroprusside, the changes of all the above fluorescence parameters under the stress condition were inhibited in different degree. The results suggest that, nitric oxide treatment can alleviate the decrease of photosynthetic rate induced by non-stomata factors and the damage of photosynthesis system, and improve the foliar photosynthetic ability under a acid rain stress condition. Increasing of photochemical efficiency and the non- photochemical dissipation of excess light energy is probably one of mechanisms which nitric oxide alleviates the damage of photosynthetic apparatus by acid rain.